This invention generally relates generally to diagnostic medical imaging and to methods and systems for storing cardiac images and ECG waveforms. More particularly, the invention relates to methods and systems for selecting images for heart analysis based on ECG waveform characteristics, thereby allowing more efficient diagnosis by the trained professional.
A coronary angiogram (or arteriogram) is an x-ray of the arteries located on the surface of the heart (the coronary arteries). Such images help the physician to see if any artery is blocked, usually by fatty plaque. If the artery is blocked, the patient may be diagnosed with coronary artery disease (“CAD”).
A coronary angiogram is often acquired along with other catheter-based tests as part of a procedure called cardiac catheterization, which includes measurement of blood pressure, taking samples for blood tests, a coronary angiogram and a left ventriculogram. In order to take an angiogram, the physician needs to inject a special dye (contrast medium) into the coronary arteries. To do this, the physician inserts a thin tube (catheter) through a blood vessel, usually in the femoral artery (groin/upper thigh area), arm or wrist, all the way up through to the heart. Once the catheter is in place, the physician can inject the dye through the catheter and into the coronary arteries. Then the x-ray can be taken.
Depending on what the angiogram shows, the physician may recommend treatments such as medication, a catheter-based procedure (e.g., a balloon angioplasty or coronary stenting) or surgery (e.g., bypass surgery). A coronary angiogram (or arteriogram) is one of the most accurate tests in the diagnosis of CAD, and over a million coronary angiograms are taken each year. The angiogram is used to pinpoint the location and severity of CAD. For example, it could reveal blockage in an artery due to either a build-up of plaque or abnormalities in the wall of the heart.
The above-described cardiac angiography is typically performed in a surgical imaging area called a cardiac catheterization laboratory. The images are acquired using cardiovascular x-ray imaging equipment The resulting images are stored and viewed on film or, increasingly, kept in digital form as DICOM (Digital Imaging and Communications in Medicine) images and stored and viewed electronically. These digital images are available for review and analysis at a physician review workstation.
During catheterization procedures, the patient also undergoes physiological monitoring using a hemodynamic monitoring system. The hemodynamic monitoring system hooks up to a patient via externally placed leads that monitor the electrical impulses from the heart and records the heart's electrical activity in the form of a waveform. This record, called an electrocardiogram (ECG), is analyzed by well-known software that measures the heart's rhythms and electrical impulses, allowing the physician to detect heart irregularities, disease and damage. The ECG data, including waveforms and results of analysis, is typically stored in a computer database.
Quantitative image analysis refers to methods of measuring angiographic images. Typically, these images are dynamic, needing to be “filmed” as the radiographic opaque dye is injected, and are reviewed for diagnosis in moving picture format. Quantitative image analysis is largely a manual process. The cardiologist will normally search through a serial run of angiographic images and move the images backward and forward until the cardiologist is satisfied that he/she has found an image representing what the cardiologist is seeking (e.g., the systolic or diastolic images). This takes valuable time that could be used in treating the patient.
Once the correct angiographic image has been selected, quantitative image analysis can be performed. A well-known analysis technique is left ventricular analysis (wall motion, ejection fraction and volume). A left ventricular analysis is carried out as follows. Dye is injected into the left ventricle at the same time the imaging system is activated. Typically, the resulting images are captured in a digital format and redisplayed through the imaging equipment. The user selects the largest (diastole) frame and the smallest (systole) frame and uses an analytical process (software) to compare the two traces. The outcome is an ejection fraction or a value that reflects the patient's heart pumping capability and may include a calculation of the actual volume pumped with each beat.
There is a need for a system that facilitates automated selection of the correct image or images for quantitative image analysis. For example, quantitative coronary analysis typically requires selection of a stored frame of imaging data acquired from a patient concurrent with a predetermined event in the patient's cardiac cycle, the latter being indicated by a feature or characteristic on a stored ECG waveform of the patient. However, synchronization of imaging data and physiologic data, both retrieved from storage, for a given study is problematic and time consuming. More specifically, the respective time stamps on the imaging and physiologic data must be synchronized. An automated frame selection technique that takes into account the need for network time synchronization is desirable.